social/mail_compose_select_lang/wizard/mail_compose_message_view.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>

        <record model="ir.ui.view" id="email_compose_message_wizard_inherit_form_lang">
            <field name="name">mail.compose.message.form.lang</field>
            <field name="model">mail.compose.message</field>
            <field name="inherit_id" ref="email_template.email_compose_message_wizard_inherit_form" />
            <field name="arch" type="xml">
                <xpath expr="//field[@name='template_id']/.." position="before">
                    <div>Force language
                        <field name="lang"
                               class="oe_inline"
                               options="{'no_create': True}"
                               on_change="onchange_lang(lang, template_id, composition_mode, model, res_id, context)"
                                />
                    </div>
                </xpath>
            </field>
        </record>

    </data>
</openerp>